Compatible permanent magnet or reluctance brushless motors and controlled switch circuits

ABSTRACT

Brushless motors have physical and electrical characteristics to be compatible with energization by the simple square or stepped wave voltages easily produced with inverter type motor control circuits having a small number of controlled switches responsive to a rotor position sensor. These motors employ a few pairs of opposing non-distributed stator windings arranged overlapping or non-overlapping with a predetermined winding pitch, and a constant gap magnetically polarized or non-polarized rotor with pole faces having related angular dimensions, to thereby produce rectilinear back emf voltages with approximately the same wave shape as the energizing voltages. The circuits can control the applied voltage to adjust motor speed.

United States Patent 1151 3,678,352 Bedford 1451 July 18, 1972 54]COMPATIBLE PERMANENT MAGNET 3,159,777 12/1964 Manteuffel ..3l8/l38 ORRELUCTANCE BRUSHLESS MOTORS AND CONTROLLED SWITCH CIRCUITS [72]Inventor: Burnice D. Bedlord, Scotia, NY.

[73] Assignee: General Electric Company [22] Filed: Nov. 6, 1970 [21]Appl. No.: 87,484

[52] U.S. Cl ..3l8/l38, 318/254 [51] Int. Cl. ..H02k 29/00 [58] Field ofSearch ..318/l38, 254, 696, 685

[56] References Cited UNITED STATES PATENTS 3,482,156 12/1969 Porath..318/138 3,023,348 2/1962 Cox ..318/l38 3,127,548 3/1964 VanEmden.....3l8/696 Primary Examiner-Gene Z. Rubinson Attorney-Paul A. Frank, JohnF. Ahem, Julius J. Zaskalicky, Donald R. Campbell, Frank L. Neuhauser,Oscar B. Waddell and Joseph B. Forman [57] ABSTRACT Brushless motorshave physical and electrical characteristics to be compatible withenergization by the simple square or stepped wave voltages easilyproduced with inverter type motor control circuits having a small numberof controlled switches responsive to a rotor position sensor. Thesemotors employ a few pairs of opposing non-distributed stator windingsarranged overlapping or non-overlapping with a predetermined windingpitch, and a constant gap magnetically polarized or non-polarized rotorwith pole faces having related angular dimensions, to thereby producerectilinear back emf voltages with approximately the same wave shape asthe energizing voltages. The circuits can control the applied voltage toadjust motor speed.

9 Claim, 12 Drawing Figurts PATENTED Jun 8 1912 SHEEI 3 [IF 5 Pmmmuuemz3,678,352

[77 Venor Barn/0e D. Eedford COMPATIBLE PERMANENT MAGNET OR RELUCTANCEBRUSIILESS MOTORS AND CONTROLLED SWITCH CIRCUITS This invention relatesto brushless permanent magnet and reluctance electric motors, and moreparticularly to brushless motors designed for efficient operation bymotor control circuits using a few controlled switches that producesimple square or stepped voltage wave shapes. These brushless motors arespecially designed to have similar back emf voltages and are suitablefor adjustable speed operation.

Conventional motors are constructed to be operated by sine wavevoltages. Motors traditionally classed as alternating current motors aredesigned to produce sine wave back electromotive force voltages since,as is well known, a motor operates most efficiently when the wave shapeof the back emf and energizing voltage are approximately the same tothereby avoid high circulating currents and consequent losses. To thisend, ordinary motors such as the a-c induction motor use dis tributedstator windings to approximate a sine wave and use stator poles that arerounded outwardly at either end of the pole face to attain the sameobjective. It is also common to use stator slots that are skewed withrespect to the axis to cause a rounding of the generated emf. At thepresent time the attempt is frequently made to use a stepped waveinverter to energize such a conventional motor. Although it is possibleto select an inverter with a large number of controlled switches thatproduce a great number of steps to approximate a sine wave, lessexpensive inverters generate fewer step changes that deviatesubstantially from a sine'wave. The less complex square or stepped waveinverters thus do not make a good combination with an a-c inductionmotor.

The permanent magnet and reluctance motors which form the subject of theinvention have similarities to motors known in the art as brushless orcommutatorless direct current motors. In the brushless d-c motor, thedrive coils carrying the magnetizing current which result in theproduction of torque are located on the stator housing rather than onthe movable rotor as in the conventional direct current motor. The rotoris commonly a permanent magnet rotor, and the circuit energizing thedrive coils uses controlled switches to control the application ofvoltage to the stator windings in a sequence to produce continuousrotation of the rotor. As a result, the commutators and brushes utilizedon the conventional motor to supply current to the armature windings iseliminated together with such undesirable features as the need toreplace brushes, arcing between commutator segments, and repair of worncommutator segments. In order to reduce the cost of the control circuit,and thus minimizethe cost of the combination of brushless motor andcontrol circuit, it is desirable to employ a simple control circuitusing a small number of controlled switches to produce simple square orstepped voltage wave shapes. Although brushless motors operated by motorcontrol circuits comprising only a few controlled switches have appearedin the prior art, there is inadequate recognition in the prior art ofthe need to match the physical and electrical parameters of the motor tothe particular rectilinear energizing voltage that can be easilyproduced by a simple control circurt.

The compatible brushless motors and motor control circuits described inthis application employ, as illustratory embodiments of the invention,motor control circuits with four to six controlled switches forproducing simple square and stepped voltage wave shapes, together withappropriate designs of permanent magnet or reluctance brushless motorsthat generate a similar back emf wave shape, whereby efficient motoroperation is obtained. As a continuation of the general subject matter,another concurrently filed application by the same inventor assigned tothe same assignee, Docket Ser. No. 87,565, filed Nov. 6 l970, disclosesand claims other brushless reluctance motors suitable to be energized byeven simpler control circuits having as few as two or three controlledswitches, wherein efficient operation is possible because reluctancemotors have no'characteristic back emf and can operate on a variety ofwave shapes.

Accordingly, an object of the invention is the improved combination of abrushless or commutatorless electric motor and a motor control circuitemploying only a few controlled switches to produce simple square orstepped voltage wave shapes, wherein the brushless motor is designed tohave the same back emf wave shape and operate efficiently on the voltageand current wave shapes produced by the particular control circuit.

Another object is the provision of a family of new and improvedpermanent magnet or reluctance brushless motors constructed to becompatible with the simple rectilinear voltage wave shapes easilyproduced by motor control circuits comprising a small number ofcontrolled switches.

Yet another object is to provide the combination of an inexpensive,efficient permanent magnet brushless motor and inverter type controlcircuit that is suitable for adjustable speed operation.

A further object is the provision of new and improved permanent magnetand reluctance brushless motors designed to be operated by the simplerectilinear wave shapes easily produced by simple inverter controlcircuits.

In accordance with the invention, a compatible brushless motor and motorcontrol circuit includes an annular stator member supporting a pluralityof opposing pairs of concentrated (non-distributed) stator windings forgenerating magnetic fields of opposite polarity in torque producingrelation to a rotatable ferromagnetic polarized or non-polarized rotor.The stator member and rotor each have opposing arcuate pole facesestablishing an approximately constant gap width therebetween. The motorcontrol circuit comprises only a few controlled switches, preferablyonly one alternately conducting pair of solid state switches for eachpair of stator windings, for applying simple substantially rectilinearwave shape energizing voltages to the pairs of stator windings. Thewinding pitch and location relative to one another of the concentratedstator windings, and circumferential length of the rotor pole faces,have interdependent angular dimensions to produce rectilinear back emfvoltages in each pair of stator windings that have approximately thesame wave shape as the applied energizing voltages. Control meansresponsive to the instantaneous rotor position renders the controlledswitches conductive for desired intervals to energize the pairs ofstator windings in a sequence to produce continuous torque to rotate therotor in a given direction.

The invention is also directed to the brushless motor per se. In variousforms of the invention, thereare two or three pairs of overlapping andnon-overlapping concentrated stator windings with a winding pitch ofabout 60, and and the rotor pole faces selectively have one of theseangular dimensions.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of several preferred embodiments of the invention, asillustrated in the accompanying drawings wherein:

FIG. 1a shows a diagrammatic end view of a permanent magnet brushlessmotor constructed in accordance with the inventionwith four 90 statorpoles and concentrated stator windings, and two 90 rotor poles;

FIG. lb is a schematic circuit diagram of a motor control circuitemploying four controlled solid state switches that is compatible withthe FIG. Ia motor;

FIG. 1c is a waveform diagram of the two phase square voltage waveformsproduced by the motor control circuit of FIG. lb, further showing indotted lines the average magnetic flux characteristics produced by theseapplied voltages;

FIG. 2a illustrates a second embodiment of a permanent magnet brushlessmotor having six overlapping 90 concentrated stator windings, and 90rotor poles;

FIGS. 2b and 20 show respectively a motor control circuit comprising sixSCRs arranged in the form of a conventional full wave, three phaseinverter circuit with the addition of a neutral switch which when closedand operated to generate the square wave voltage wave shapes andresultant magnetic flux curves shown in FIG. 20 is suitable to energizethe FIG. 2a motor;

FIGS. 3a and 3b illustrates respectively another embodiment of thepermanent magnet brushless motor with six overlapping 120 concentratedwindings and a 120 rotor that is energized by the control circuit ofFIG. 2b, the neutral switch assumed to be open, in a manner to producethe three phase stepped voltage wave shapes and resulting averagemagnetic flux characteristics shown in FIG. 3b;

FIG. 4a is still another embodiment of a permanent magnet brushlessmotor characterized by six 60 non-overlapping concentrated windings anda 120 rotor;

FIGS. 4b and 40 show respectively the quasi-square voltage wave shapessupplied to three adjacent stator windings of the FIG. 4a motor by themotor control circuit of FIG. 2b when modified to have delta-connectedpairs of stator windings as illustrated in FIG. 40; and

FIG. 5 is a modified form of the motor shown in FIG. 4a having sixoverlapping 120 windings and a 120 reluctance rotor, that is suitablefor energization by the same voltage wave shapes as illustrated in FIG.4b.

The compatible brushless motor designs and motor control circuits to bedescribed are suitable for manufacture in the small to medium horsepowerrange. These motors are preferably made with permanent magnet rotors,shaped to create a constant air gap at the interface with the statorpole faces, but can also be made with reluctance type soft iron rotorshaving a similar shape. In some applications, the higher manufacturingcost of the permanent magnet motor is justified to save weight andpower.

FIG. 1a shows a permanent magnet motor in a size suitable for operationfrom a battery source by a motor control circuit that uses fourcontrolled switches for producing a two phase square voltage wave shape.The motor comprises in general an annular stator member 11 including aframe member 14 within which a permanent magnet rotor 52 rotates on ashaft 13. The permanent magnet rotor 52 has diametrically opposite 90arcuate pole faces and two parallel sides, and preferably has laminatedpole tips to prevent hysteresis and eddy current loss due to variationsof the flux at the pole surfaces. The stator frame member 14 is providedwith four equally spaced winding slots 53 shaped to have small openingsto provide a good flux path for the rotor flux and to define statorsegments or pole faces 1Sa-l5d that have an almost 90 circumferentiallength. It will be noted that the entire length of each stator segmentis arcuate, i.e., the ends are not rounded outwardly toward the outsideof the motor. Two opposing pairs of stator windings are supported on thestator frame 14 within the slots 53, each with a 90 winding pitch.

Referring to the motor control circuit shown in FIG. lb, stator windings54A and 54A are essentially a single winding wound in two adjacentstator slots, while windings 54B and 54B are wound effectively as asingle winding in the opposing stator slots. Electrically, the centertap junctions between windings 54A and 54A and between windings 54B and54B, are connected together and to positive supply terminal 20. Theother free ends of the respective pairs of windings so formed arecoupled to negative supply terminal 21 respectively through transistorswitch 56'and inverse parallel connected diode 57, and throughtransistor switch 58 and its associated feedback diode. Supply terminals20 and 21 are connected across a battery 25 and parallel filtercapacitor 26. Since windings 54A and 54B conduct current in only onedirection, they are wound oppositely to produce opposite magnetic poles,and the same is true of windings 54A and 548'. The other pairs of theopposing windings 55A and 55A, and 55B and 55B, are displacedmechanically by 90, but are otherwise identically arranged and connectedwith the use of the third and fourth transistors 59 and 60 and theirrespective inverse-parallel feedback diodes.

Gating circuit 61 for the four transistors is under the control of amechanical, magnetic, or optical rotor position sensor, to initiateswitching of the transistor switches as the motor rotates in dependenceupon the instantaneous position of rotor 52. Specific gating circuitsthat can be used are given, for example, in the Transistor Manual, 7thEdition, copyright I964, published by the General Electric Company andavailable from the Semiconductor Products Department, Electronics Park,Syracuse, New York. The rotor position sensor illustrated in FIG. 1acomprises a plurality of magnetic sensors in the form of Hall elementsor generators 46-49 assembled at intervals about an extension of themotor shaft 13 and actuated by a permanent magnet 50 secured forrotation with shaft 13. Sensors of this type which operate on the Halleffect principle generate an output voltage between the two outputterminals when a magnetic field is applied perpendicular to the face ofthe Hall element and an energizing control current is applied betweenthe two input terminals, which are usually aligned with the longitudinalaxis of the element. Further information on the Hall generator itselfand its utility as a rotor position sensor in a brushless motor can beobtained from the prior art patents, as for example, US. Pat. No.3,159,777 to E.W. Manteuffel, granted Dec. 1, 1964, and assigned to theGeneral Electric Company. As has been indicated, a mechanical cam or anoptical sensor, as is known in the art, can also be used to sense theinstantaneous position of permanent magnet rotor 52 whereby gatingcircuit 61 provides gating signals for transistors 56, 58, 59, and 60that are timed in dependence upon the rotor position. This directcontrol of the time of switching of the control switches makes the motorfunction much as a d-c motor with no synchronizing problems.

The permanent magnet motor of FIG. la is symmetrical and is operable inboth directions. The compatible motor control circuit of FIG. 1b iscontrolled to apply to the opposing pairs of stator windings the twophase square wave voltage wave shapes illustrated in FIG. 1c forwindings 54A and 55A, the wave shapes for the other pair of opposedwindings being similar. The voltage wave shapes and average magneticflux characteristics, shown in dotted lines, are idealized, and thediscussion of the motor to follow assumes idealized parameters andcharacteristics. The motor air gap and control circuit switching timesmay depart slightly from the idealized situation to compensate forleakage flux and flux shift due to motor torque. The same remarks applyto FIGS. 2a-5. Each stator winding and its associated stator pole actslike a simple solenoid in that the magnetic flux characteristic producedby the application of a constant unidirectional voltage is linear. Themagnetic flux characteristics da and (1: A generated respectively by theapplication of square wave voltages E and E increase and decreaselinearly in the manner shown in FIG. 10. Switching of the transistors inthe control circuit to change the polarity of the applied voltage istimed such that the rotor 52 is centered on a particular stator polewhen the flux in that stator pole is at a maximum. Accordingly,transistors 56 and 58 change state almost simultaneously, i.e., theconducting one is turned off and the non-conducting one is turned on,when rotor 52 is centered and stator poles 15a and 150. In like manner,transistors 59 and 60 are operated as a complementary pair and changestate when rotor 52 is centered on the other two stator poles 15b and15d.

In a typical sequence of operations for counter-clockwise rotation,transistor 56 is turned on to establish current flow through statorwindings 54A and 548 when a reference end of the rotor (the S pole) iscentered on stator pole 150. Looking only at the state of the flux instator pole 15a, it is seen that the average flux is driven from itsmaximum negative value and crosses the zero ordinate just at the timethat the leading edge of permanent magnet rotor 52 reaches the near endof stator,

pole 15a, adjacent to stator pole 15d. During the next onequarter ofrevolution when the arcuate pole face of rotor 52 is moving intoalignment with stator pole 15a, the average magnetic flux in this statorpole increases from about zero to its maximum. At this time the state oftransistors 56 and 58 is changed, and transistor 58 is now conductiveand energizes windings 54A and 54B. During the succeeding one-quarter ofrevolution of rotor 52, the average flux in stator pole 15a isdecreasing linearly from its maximum to zero, and the polarity of theflux changes just as the trailing end of rotor 52 leaves the end ofstator pole I5a adjacent to stator pole 15b. The

magnetic flux in the orthogonally oriented stator pole d is tracing asimilar characteristic but delayed by 90 as related to the rotation ofthe rotor, and so on for the other stator poles. Thus, continuous torqueis exerted upon rotor 52.

When the FIG. 1a motor is used as a permanent magnet motor, the rotorflux is relatively constant and the motor tends to have thevoltage-speed characteristics of a d-c shunt motor. If the permanentmagnet rotor is replaced by a reluctance rotor, the motor runs as avariable reluctance motor and has the voltage-speed characteristics thattend to be more like those of series d-c motors. Magnetic saturation maybe used to limit the flux and obtain a characteristic which is acompromise between that of a series and a shunt motor. Either the seriesor shunt motor characteristic is suitable for speed control bycontrolling the d-c voltage. To vary the d-c supply voltage, and thuschange the speed of the motor, it is possible to use a time ratiovoltage control circuit ahead of the motor to change supply voltage forthe motor windings, or a single phase alternating current source can beused in conjunction with a phase controlled rectifier. The motorswitching circuit of FIG. lb, however, is well suited to include timeratio voltage control. To do this, a transistor switch that isconducting is turned on and off rapidly at a fast rate compared to themotor speed to control the average motor voltage and motor current. Theassociated feedback diode 57 is conductive during the short period whenthe transistor is turned off to achieve time ratio control. Thus, gatingcircuit 61 is optionally under the control of time ratio control circuit38. The reduction of the voltage applied to the pairs of statorwindings, as is well known, depends upon the ratio of the time it isconducting to the time it is non-conducting as it is being turned on andoff rapidly.

The permanent magnet or reluctance motor and motor control circuit arecompatible because the brushless motor constructed as shown in FIG. lagenerates approximately the same back emf voltage wave shape as isapplied to the pairs of stator windings by the motor control circuit ofFIG. 1d. This assumes that there is constant air gap between the rotorpole faces and the stator pole faces. To illustrate this, the back emfvoltage wave shape generated in stator winding 54A will be traced(assuming an ideal motor) during one-half revolution of rotor 52.Looking only at one end of the rotor, as for instance, the north pole,the average magnetic flux generated in stator pole 15a increaseslinearly from zero to a maximum and then back to zero as rotor 52rotates 90 clockwise from out of alignment into complete alignment withstator pole 15a, and then another 90 from complete alignment to out ofalignment in the other direction. At this time the south pole of rotor52 is' beginning to move into alignment with stator pole 15a, and duringthe next one-half revolution the magnetic flux decreases linearly fromzero to a minimum in the other direction and back to zero. Consequently,the back emf voltage generated in stator winding 54A has the same squarevoltage wave shape as that for the energizing voltage shown in FIG. 1c,and the phasing is the same. Of course, a suitable technique is used toassure that the motor has running current, such as by making themagnitude of the applied voltage greater than the back emf voltage andthe IR drop involved in circulating current through the stator windings.Also, the switching times of the switches with respect to rotor positionmay be advanced to compensate for leakage reactance, or some departurefrom the idealized air gap may be made to compensate for leakage fluxand flux shift due to load current or flux shift due to motor torque. Tobe compatible with two phase square wave voltage energization of themotor, and to avoid the excessive circulating currents and losses thatare incurred when the back emf voltage wave shape is not the same as theapplied voltage wave shape, it is seen that the FIG. la motor isconstructed with non-overlapping approximately 90 concentrated statorwindings, and a rotor with arcuate pole faces that have an effectivecircumferential length of about 90' also. The brushless motorconstructed in this manner operates efficiently on applied voltages witha two phase square wave shape.

The second embodiment of the invention shown in FIG. 2a also uses apermanent magnet rotor, however there are now six overlapping 90concentrated stator windings, and different combinations of 30 statorsegments forming 90 stator poles. The combinations of stator segments,it is understood, become a pole under the influence of windingmagnetomotive force and in dependence on the position of the rotor. Thisbrushless motor is energized by what can be referred to as three phasesquare voltage wave shapes, and this motor design produces a similarback emf wave shape. The three pairs of opposing 90 concentrated statorwindings are identified as windings 64A and 64A, 64B and 64B, 64C and64C. A total of l2 stator slots 53 are located about the inner peripheryof stator member 14, defining 12 equal stator segments, and each windingdisposed in the stator slots overlaps the two adjacent windings by 30.The three phase square voltage wave shapes required for efficientoperation of the motor of FIG. 2a are shown in FIG. 2c, and can beproduced by what can loosely be called a three-phase version of the FIG.lb control circuit. Another compatible motor circuit for producing thistype of voltage wave shape is the motor control circuit of FIG. 2b,which is energized by a three phase alternating current source, uses aphase controlled rectifier for input voltage control, and employs sixsilicon controlled rectifiers as the power switching devices arranged asa conventional three phase inverter circuit.

Referring to FIG. 2b, the input terminals of the motor control circuitare connected to a conventional full wave, phase controlled rectifier 65comprising six SCRs. As is well known, varying the phase of which theSCRs are rendered conductive adjusts the magnitude of the d-c voltageproduced at output terminals 66 and 67. The motor control circuit properis a full wave, three phase inverter circuit. The first phase comprisestwo SCRs 68 and 69 connected in series with a current limiting andcommutating winding 70, and further includes a feedback diode 71 forreactive current connected in inverse-parallel relationship across theload terminals of each thyristor. The center tap point x of commutatingwinding 70 is coupled directly to series connected stator windings 64Aand 64A, which are optionally connected through a neutral switch 72 tothe junction between two series connected voltage divider capacitors 73and 74. The other two phases of the inverter circuit have an identicalarrangement of components designated by the same numeral with an a or bsuffix. The three pairs of opposing stator windings are Wye-connected toone terminal of neutral switch 72, and to respective commutating windingcenter tap points x, y, and z in the three phases of the invertercircuit. I

The silicon controlled rectifier is a triode reverse blocking thyristorthat is rendered conductive when the anode is positive with respect tothe cathode and when a gating signal is applied to the gate electrode.Thereafter the gate electrode loses control over conduction through thedevice and to commutate it off or render it non-conductive it isnecessary to apply a reverse bias voltage or to reduce the flow ofcurrent through the device below the holding value for a determined timebefore reapplying forward voltage. Gating signals and commutatingimpulses for the thyristors are generated in a circuit 75 under thecontrol of a mechanical, magnetic, or optical rotor position sensor 37of the type previously discussed with regard to FIG. la. Suitable gatingcircuits that can be used are given in the Silicon Controlled RectifierManual, 4th Edition, copyright 1967, published by the General ElectricCompany, and available from the address previously given. Thecommutating impulses are coupled respectively to commutating windings70, 70a, and 70b by closely coupled windings 76, 76a, and 76b. Thecommutating pulses generate reverse currents that oppose the flow ofload current through a conducting SCR to commutate it off. In order toproduce the square voltage wave shapes shown in FIG. 2c, it is necessaryto close neutral switch 72. The operation of this type of invertercircuit, which operates on simple square wave gating signals, is wellknown as described for example in the book, Principles of InverterCircuits" by Bedford and I-loft, John Wiley and Sons, Inc.,

New York, Library of Congress catalog card No. 64-20078, copyright 1964.Briefly, supplying a gating signal from circuit 75 to the gate electrodeof SCR 68 to render it conductive applies a positive polarity squarewave voltage to windings 64A and 64A, which are wound in oppositedirections to produce opposite magnetic poles. Upon commutating off SCR68 and turning on SCR 69, the polarity of the voltage applied towindings 64A and 64A is reversed, thereby reversing the polarity of thestator magnetic poles produced when the flow of current through thewindings changes direction. The other thyristors in the other phases ofthe inverter are operated similarly at the proper intervals to producethe 60 phase displaced square voltage wave shapes shown in FIG. 20. Onlyvoltage waveforms E E and E representing the voltages applied to thosewindings are illustrated, the others being complementary.

Each opposing pair of stator windings is alternately energized withpositive polarity voltage and negative polarity voltage at 180 intervalsof rotation of permanent magnet rotor 52. The timing of application ofvoltage is the same as described with regard to FIGS. Ia-lc, that is,the change from one polarity to the other is made when an adjacent rotorpole is approximately centered on a particular concentrated winding andthe stator pole defined by that winding. As is also the case with FIG.1c, the flux at the instant at that particular stator pole isapproximately at a maximum. As will be observed in FIG. 20, where theaverage magnetic flux characteristics (p (b and (1) are illustrated, themagnetic flux in any particular pole increases and decreases linearly.The motor shown in FIG. 2a is, loosely speaking, a three-phase versionof the two phase motor of FIG. 1a, and operates in a similar manner. Theonly difference is that the stator windings overlap by 30 on eachside,'and consequently, the total average magnetic flux in theseoverlapping stator pole regions is the sum of the flux produced by eachstator winding operating individually. The flux due to the overlappingwindings is of the same polarity during most of the time that anyportion of the rotor is adjacent that stator pole portion, and thus isbeneficial since it tends to smooth the torque. For example, the flux inthe stator segment between stator slots 1 and 2 is the sum of that dueto stator winding 64A and stator winding 64C. At the time the flux inthis stator segment produced by winding 64A is going through zero towardits maximum (the leading end of rotor 52 is adjacent stator slot No. I),the flux generated by stator winding 64C is increasing toward the samepolarity maximum and does not begin to decrease until the leading end ofrotor 52 is adjacent stator slot No. 2. The overlapping stator winding,therefore, is beneficial to the production of continuous torque.

The motor constructed as illustrated in FIG. 2a is compatible with themotor control circuit of FIG. 2b when connected and controlled toproduce the voltage wave shapes shown in FIG. 2c because the motoroperates efficiently with these applied voltage wave shapes, as hasalready been explained, while at the same time the back emf generated inthe stator windings have the same wave shape. In the same manner as hasbeen discussed with regard to FIGS. la-lc, the rotor flux acting on eachopposing pair of concentrated stator windings increases linearly to amaximum and then decreases linearly to the same level as the rotor polesrotate 180 from out of alignment into complete alignment, and then fromcomplete alignment to out of alignment in the other direction. Thisinduces a square voltage wave shape or square back emf in each statorwinding pair. Since the pairs of stator coils are physically displacedby 60, the resulting back emfs are also phase displaced by 60 as relatedto the rotation of the motor, and this corresponds to the three phasesquare wave voltage energization of the stator windings illustrated inFIG. 2c. Adjustable speed operation of this motor and of the othermotors to be described hereafter that are operated by the FIG. 2bcontrol circuit is obtained, as previously mentioned, by control of thedo supply voltage by the phase controlled rectifier. The voltageimpressed on the stator windings is also changed by time ratio controloperation of the thyristor switches. Moreover, the SCRs in this controlcircuit can be replaced by other suitable solid-state switches such asthe transistor, diac, triae, etc.

The conventional three phase stepped wave voltage wave shapes shown inFIG. 3b are obtained when the neutral switch in the motor controlcircuit of FIG. 2b is opened and the inverter is operated according tothe widely used mode of operation as described for instance in theaforementioned Bedford and Hoft book. InFlG. 2b, it is assumed thatwindings 78A and 78A replace windings 64A and 64A, and so on. Thecompatible motor design for use with these voltage wave shapes isillustrated in FIG. 3a. The three pairs of opposing concentrated statorwindings 78A and 78A, 78B and 78B, and 78C and 78C, are located so as tooverlap each adjacent winding by 60. To this end there are six of thestator slots 53, equally spaced from one another, defining six equalstator segments. The permanent magnet rotor 79 has 120 arcuate rotorpole faces.

The three phase stepped voltage wave shapes E E and E illustrated inFIG. 3b, are phase displaced by 60 as related to the revolution of themotor. The corresponding magnetic flux characteristics 41 and 4),produced by these energizing voltages are also shown in dashed lines inFIG. 3b. The application of voltage to a particular stator winding istimed so that the change from positive to negative polarity of appliedvoltage occurs when the flux produced by that stator winding is at amaximum and the rotor is centered on that particular winding orcompletely aligned with it. Subsequent step changes in the appliedvoltage are made at 60 intervals as related to the revolution of themotor. With the use of a 120 rotor and a 120 concentrated statorwinding, there may be some negative torque exercised on the rotor duringone-quarter of the time that any portion of a rotor pole face isopposite any portion of the corresponding stator pole face. This isbecause the rotor takes 120 to rotate into alignment with the statorpole, and 120 to rotate out of alignment, making a total of 240, whereasthe magnetic flux in any particular stator winding is changing at 180intervals. During a 60 interval, then, negative torque may be exerted onthe rotor, depending on such factors as the leakage reactance, etc., asis known in the art. However, some negative torque is not detrimental togood operation of the motor. In the manner already explained with regardto FIG. 2a, the use of overlapping stator windings in general isbeneficial because of the smoother torque produced.

The back emf wave shape produced by a permanent magnet or reluctancemotor constructed as shown in FIG. 3a is the same as the applied stepvoltage wave shapes, and hence the motor and control circuit arecompatible. During any single 180 interval of travel of the rotor past aparticular concentrated stator winding, such as winding 78A, and in viewof the 120 circumferential length of the rotor pole faces, there is aperiod when one rotor pole is acting on the stator winding, a periodwhen both rotor poles are acting on the stator winding, and a periodwhen the other rotor pole is acting on the stator winding solely.Assuming that the leading edge of the north pole of rotor 52 iscommencing to rotate clockwise into alignment with concentrated winding78A, the aligned rotor poles at 60 intervas are: S 60, N 60, N 120, N60, and S 60". This plots out a magnetic flux characteristic acting onconcentrated stator winding 78A that is identical to the curve da inFIG. 3b. The resulting induced back emf has the same wave shape asapplied voltage E The permanent magnet motor designs illustrated in FIG.4a and FIG. 5a are both compatible for energization by the voltage waveshapes shown in FIG. 4b. These quasisquare voltage wave shapes areproduced when the motor control circuit of FIG. 2b is operated with theneutral switch open with with the three pairs of stator windingsdelta-connected as shown in FIG. 4c. To obtain these quasi-squarevoltage wave shapes, in which the zero voltage intervals are half aslong as the positive and negative voltage intervals, the thyristors aresupplied with 180 square wave gating signals and are sequentially gatedat 60 intervals in the manner further explained on page 267 of theaforementioned Bedford and Hoft book.

The compatible motor design of FIG. 4a uses the 120 permanent magnetrotor 79, but requires three pairs of opposing 60 concentrated statorwindings 80A and 80A, 80B and 80B, and 80C and 80C that arenon-overlapping. The three applied voltage wave forms E E and Eillustrated in FIG. 4b are phase displaced by 60 as related to therevolution of motor, corresponding to the physical displacement of theopposing pairs of stator windings. As is observed from the magnetic fluxcharacteristics 41 and (p the fiux is driven to a maximum of onepolarity by the applied voltage, and remains at this maximum levelduring the zero voltage interval, and is driven down only by applying avoltage of the opposite polarity. The switching of the thyristors in themotor control circuit occurs at intervals about 30 before and after thecenter of the rotor pole face is at the center of a particularconcentrated winding, since both the flux and the applied voltage areconstant during the intervening 60 interval. Efficient operation of themotor is obtained as the magnetic flux in succeeding stator poles in aclockwise or counterclockwise sequence are driven to their constantmaximum value at succeeding 60 intervals. No negative torque is producedsince the entire 120 permanent magnet rotor 79 requires exactly 180 torotate past every portion of a 60 stator pole.

The back emf voltages produced by the motor of FIG. 4a have the samequasi-square voltage wave shapes as the applied voltages illustrated inFIG. 4b. Going through the analysis for concentrated stator winding 80B,the rotor fiux acting on stator winding 80B increases linearly, assumingclockwise rotation, as the leading edge of rotor 79 rotates from statorslot No. 1 to stator slot No. 2. For the next 60 rotation, the rotorflux is constant, while for the remaining 60 of rotation, the fiux isdecreasing linearly back towards zero. This is the same characteristicas the flux characteristics shown in FIG. 4b, and the induced back emfgenerated in stator winding 808 has the same wave shape as the appliedvoltage wave shape.

The motor design of FIG. is also compatible with the FIG. 2b motorcontrol circuit when operated to produce-the quasisquare voltage waveshapes given in FIG. 4b. In place of the 120 permanent magnet rotor 79,the rotor 81 has a 60 circumferential length and is illustrated as beinga soft iron reluctance rotor in place of the permanent magnet rotor. Thethree pairs of opposing concentrated 120 stator windings are identicalto the stator winding arrangement shown in FIG. 3a, and for convenienceare given the same identifying numerals. These concentrated 120 statorwindings overlap each adjacent winding by 60. The timing of the appliedvoltage to a particular stator winding is such that the magnetic flux inthat stator pole, taken individually, is midway through its constantmaximum magnitude at the time the rotor 81 is centered upon thatparticular stator winding. No negative torque is exerted upon rotor 81,and the resultant flux pattern produced by the overlapping pairs ofstator windings is beneficial to the production of continuous for thereasons given in the discussion of FIG. 3a. The back emf generated bythe FIG. 5 motor in any one stator winding is the same as the appliedvoltage wave shapes. As rotor 81 rotates past stator winding 78A, forexample, the flux acting on stator winding 78A to produce an inducedback emf increases to a maximum as the stator rotates 60, is constantfor the next 60, and then decreases linearly for the final 60 ofrotation. Consequently, the motor of FIG. 5 and the motor controlcircuit of FIG. 2b, operated to produce the applied voltage wave shapesshown in FIG. 4b, are compatible.

In summary, a family of permanent magnet or reluctance brushless motorsare designed to have a simple approximately square or stepped wave shapeback emf characteristic that matches the applied voltage wave shapeseasily produced by a motor control switching circuit comprising a numberof controlled switches. The switching circuits disclosed are knowninverter-type circuits using solid state switches that can if desired becontrolled by time ratio control principles to vary the voltageimpressed on the motor windings to adjust the speed of the motor. Thebrushless motors comprise an annular stator with opposing pairs ofconcentrated (non-distributed) stator windings wound with apredetermined winding pitch in non-overlapping or overlappingrelationship. The permanent magnet or reluctance rotors have opposingarcuate poles, to define a constant or an approximately constant widthgap between the rotor and stator poles faces, and a specifiedcircumferential length. The motors are simple, but operate with goodefiiciency on rectilinear or substantially rectilinear wave shapes, ascompared to conventional alternating current motors that have designfeatures adapting them for sine wave energization.

While the invention has been particularly shown and described withreference to several preferred embodiments thereof, it will beunderstood by those skilled in the art that the foregoing and otherchanges may be made therein without departing from the spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A compatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of opposing pairs ofconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a rotatable ferromagneticrotor, said stator member and rotor each having opposing arcuate polefaces to establish an approximately constant gap width therebetween,

a motor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear wave shape energizing voltagesof both polarities to said pairs of stator windings,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesubstantially rectilinear back emf voltages in each pair of statorwindings that have approximately the same wave shape as the energizingvoltage applied by said motor control circuit, and

control means responsive to the instantaneous position of said rotor forrendering conductive said controlled switches for desired intervals ofconduction to energize said pairs of stator windings in a sequence toproduce continuous torque to rotate said rotor in a given direction,

wherein there are only three opposing pairs of series connectedconcentrated stator windings,

said motor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices,

said three opposing pairs of concentrated stator windings each having awinding pitch of about and each stator winding overlaps the adjacentstator windings by about 30, and

said rotor pole faces have a circumferential length of about 90, wherebythe brushless motor is suitable for square voltage wave shapeenergization.

2. A compatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of opposing pairs ofconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a rotatable ferromagneticrotor, said stator member and rotor each having opposing arcuate polefaces to establish an approximately constant gap width therebetween,

a motor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear wave shape energizing voltagesof both polarities to said pairs of stator windings,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesubstantially rectilinear back emf voltages in each pair of statorwindings that have approximately the same wave shape as the energizingvoltage applied by said motor control circuit, and

control means responsive to the instantaneous position of said rotor forrendering conductive said controlled switches for desired intervals ofconduction to energize said pairs of stator windings in a sequence toproduce continuous torque to rotate said rotor in a given direction,

wherein there are only three opposing pairs of series connectedconcentrated stator windings,

said motor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices,

said three opposing pairs of concentrated stator windings have a windingpitch of about 120 and each stator winding overlaps the adjacent statorwindings by about 60, and

said rotor pole faces have a circumferential length of about 120,whereby the brushless motor is suitable for stepped voltage wave shapeenergization.

3. A compatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of opposing pairs ofconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a rotatable ferromagneticrotor, said stator member and rotor each having opposing arcuate polefaces to establish an approximately constant gap width therebetween,

a motor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear wave shape energizing voltagesof both polarities to said pairs of stator windings,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesubstantially rectilinear back emf voltages in each pair of statorwindings that have approximately the same wave shape as the energizingvoltage applied by said motor control circuit, and

control means responsive to the instantaneous position of said rotor forrendering conductive said controlled switches for desired intervals ofconduction to energize said pairs of stator windings in a sequence toproduce continuous torque to rotate said rotor in a given direction,

wherein there are only three opposing pairs of series connectedconcentrated stator windings,

said motor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices,

said three opposing pairs of concentrated stator windings arenon-overlapping windings each having a winding pitch of about 60, and

said rotor pole faces have a circumferential length of about 120,whereby the brushless motor is suitable for quasisquare voltage waveshape energization.

4. A compatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of opposing pairs ofconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a rotatable ferromagneticrotor, said stator member and rotor each having opposing arcuate polefaces to establish an approximately constant gap width therebetween,

a motor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear wave shape energizing voltagesof both polarities to said pairs of stator windings,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesubstantially rectilinear back emf voltages in each pair of statorwindings that have approximately the same wave shape as the energizingvoltage applied by said motor control circuit, and

control means responsive to the instantaneous position of said rotor forrendering conductive said controlled switches for desired intervals ofconduction to energize said pairs of stator windings in a sequence toproduce continuous torque to rotate said rotor in a given direction,

wherein there are only three opposing pairs of series connectedconcentrated stator windings,

said motor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices,

said three opposing pairs of concentrated stator windings have a windingpitch of about 120 and each stator winding overlaps the adjacent statorwindings by about 60, and

said rotor pole faces have a circumferential length of about 60",whereby the brushless motor is suitable for quasisquare voltage waveshape energization.

5. A brushless motor suitable for energization by simple substantiallyrectilinear voltage wave shapes comprising an annular stator membersupporting a plurality of opposing pairs of series connectedconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a ferromagnetic rotor mountedfor rotation within said stator member, said stator member and rotoreach having opposing arcuate pole faces to establish an approximatelyconstant gap width therebetween,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesimple substantially rectilinear back emf voltages in each pair ofstator windings that have approximately the same wave shape as theenergizing rectilinear voltage wave shapes,

wherein there are three opposing pairs of concentrated stator windingseach having a winding pitch of about and each stator winding overlapsthe adjacent stator windings by about 30, and

said rotor pole faces have a circumferential length of about 90, wherebythe brushless motor is suitable for square voltage wave shapeenergization.

6. A brushless motor suitable for energization by simple substantiallyrectilinear voltage wave shapes comprising an annular stator membersupporting a plurality of opposing pairs of series connectedconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a ferromagnetic rotor mountedfor rotation within said stator member, said stator member and rotoreach having opposing arcuate pole faces to establish an approximatelyconstant gap width therebetween,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesimple substantially rectilinear back emf voltages in each pair ofstator windings that have approximately the same wave shape as theenergizing rectilinear voltage wave shapes,

wherein there are three opposing pairs of concentrated stator windingseach having a winding pitch of about 120 and each stator windingoverlaps the adjacent stator windings by about 60, and

said rotor pole faces have a circumferential length of about 120,whereby the brushless motor is suitable for stepped wave energization.

7. A brushless motor suitable for energization by simple substantiallyrectilinear voltage wave shapes comprising an annular stator membersupporting a plurality of opposing pairs of series connectedconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a ferromagnetic rotor mountedfor rotation within said stator member, said stator member and rotoreach having opposing arcuate pole faces to establish an approximatelyconstant gap width therebetween,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesimple substantially rectilinear back emf voltages in each pair ofstator windings that have approximately the same wave shape as theenergizing rectilinear voltage wave shapes,

wherein there are three non-overlapping opposing pairs of concentratedstator windings each having a winding pitch of about 60, and

said rotor pole faces have a circumferential length of about 120,whereby the brushless motor is suitable for quasisquare wave shapeenergization.

8. A brushless motor suitable for energization by simple substantiallyrectilinear voltage wave shapes comprising an annular stator membersupporting a plurality of opposing pairs of series connectedconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a ferromagnetic rotor mountedfor rotation within said stator member, said stator member and rotoreach having opposing arcuate pole faces to establish an approximatelyconstant gap width therebetween,

the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesimple substantially rectilinear back emf voltages in each pair ofstator windings that have approximately the same wave shape as theenergizing rectilinear voltage wave shapes,

wherein there are three opposing pairs of concentrated stator windingseach having a winding pitch of about and each stator winding overlapsthe adjacent stator windings by about 60, and

said rotor pole faces have a circumferential length of about 60, wherebythe brushless motor is suitable for quasisquare wave shape energization.

9. A compatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of symmetrically arrangedopposing pairs of concentrated stator windings each simultaneouslygenerating magnetic fields of opposite polarity in torque producingrelation to a rotatable ferromagnetic rotor, said stator member androtor having opposing arcuate pole faces to establish an approximatelyconstant gap width therebetween.

a motor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear stepped wave shape energizingvoltages of both polarities to said pairs of stator windings, whereinthe sum of the angular dimensions of the winding pitch of saidconcentrated stator windings and the circumferential len th of one ofsaid rotor ole faces totals approximately 24 and produces substan rallyrectilinear back emf voltages in each pair of stator windings that haveapproximately the same wave shape as the energizing voltage applied bysaid motor control circuit, and

control means responsive to the instantaneous position of said rotor forrendering conductive said controlled switches for desired intervals ofconduction to energize said pairs of stator windings in a sequence toproduce continuous torque to rotate said rotor in a given direction.

1. A compatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of opposing pairs ofconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relatIon to a rotatable ferromagneticrotor, said stator member and rotor each having opposing arcuate polefaces to establish an approximately constant gap width therebetween, amotor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear wave shape energizing voltagesof both polarities to said pairs of stator windings, the winding pitchand location relative to one another of said concentrated statorwindings, and the circumferential length of said rotor pole faces,having interdependent angular dimensions to produce substantiallyrectilinear back emf voltages in each pair of stator windings that haveapproximately the same wave shape as the energizing voltage applied bysaid motor control circuit, and control means responsive to theinstantaneous position of said rotor for rendering conductive saidcontrolled switches for desired intervals of conduction to energize saidpairs of stator windings in a sequence to produce continuous torque torotate said rotor in a given direction, wherein there are only threeopposing pairs of series connected concentrated stator windings, saidmotor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices, said three opposing pairsof concentrated stator windings each having a winding pitch of about 90*and each stator winding overlaps the adjacent stator windings by about30*, and said rotor pole faces have a circumferential length of about90*, whereby the brushless motor is suitable for square voltage waveshape energization.
 2. A compatible brushless motor and motor controlcircuit comprising an annular stator member supporting a plurality ofopposing pairs of concentrated stator windings for generating magneticfields of opposite polarity in torque producing relation to a rotatableferromagnetic rotor, said stator member and rotor each having opposingarcuate pole faces to establish an approximately constant gap widththerebetween, a motor control circuit comprising only a few controlledswitches for applying simple substantially rectilinear wave shapeenergizing voltages of both polarities to said pairs of stator windings,the winding pitch and location relative to one another of saidconcentrated stator windings, and the circumferential length of saidrotor pole faces, having interdependent angular dimensions to producesubstantially rectilinear back emf voltages in each pair of statorwindings that have approximately the same wave shape as the energizingvoltage applied by said motor control circuit, and control meansresponsive to the instantaneous position of said rotor for renderingconductive said controlled switches for desired intervals of conductionto energize said pairs of stator windings in a sequence to producecontinuous torque to rotate said rotor in a given direction, whereinthere are only three opposing pairs of series connected concentratedstator windings, said motor control circuit comprises a pair ofalternately conducting controlled switches for each pair of statorwindings, said controlled switches being solid state controlled devices,said three opposing pairs of concentrated stator windings have a windingpitch of about 120* and each stator winding overlaps the adjacent statorwindings by about 60*, and said rotor pole faces have a circumferentiallength of about 120*, whereby the brushless motor is suitable forstepped voltage wave shape energization.
 3. A compatible brushless motorand motor control circuit comprising an annular stator member supportinga plurality of opposing pairs of concentrated stator windings forgenerating magnetic fields of opposite polarity in torque producingrelation to a rotatable ferromagnetic rotor, said stator member androtor each having opposing arcuate pole faces to establish anapproximately constant gap width therebetween, a motor control circuitcomprising only a few controlled switches for applying simplesubstantially rectilinear wave shape energizing voltages of bothpolarities to said pairs of stator windings, the winding pitch andlocation relative to one another of said concentrated stator windings,and the circumferential length of said rotor pole faces, havinginterdependent angular dimensions to produce substantially rectilinearback emf voltages in each pair of stator windings that haveapproximately the same wave shape as the energizing voltage applied bysaid motor control circuit, and control means responsive to theinstantaneous position of said rotor for rendering conductive saidcontrolled switches for desired intervals of conduction to energize saidpairs of stator windings in a sequence to produce continuous torque torotate said rotor in a given direction, wherein there are only threeopposing pairs of series connected concentrated stator windings, saidmotor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices, said three opposing pairsof concentrated stator windings are non-overlapping windings each havinga winding pitch of about 60*, and said rotor pole faces have acircumferential length of about 120*, whereby the brushless motor issuitable for quasi-square voltage wave shape energization.
 4. Acompatible brushless motor and motor control circuit comprising anannular stator member supporting a plurality of opposing pairs ofconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a rotatable ferromagneticrotor, said stator member and rotor each having opposing arcuate polefaces to establish an approximately constant gap width therebetween, amotor control circuit comprising only a few controlled switches forapplying simple substantially rectilinear wave shape energizing voltagesof both polarities to said pairs of stator windings, the winding pitchand location relative to one another of said concentrated statorwindings, and the circumferential length of said rotor pole faces,having interdependent angular dimensions to produce substantiallyrectilinear back emf voltages in each pair of stator windings that haveapproximately the same wave shape as the energizing voltage applied bysaid motor control circuit, and control means responsive to theinstantaneous position of said rotor for rendering conductive saidcontrolled switches for desired intervals of conduction to energize saidpairs of stator windings in a sequence to produce continuous torque torotate said rotor in a given direction, wherein there are only threeopposing pairs of series connected concentrated stator windings, saidmotor control circuit comprises a pair of alternately conductingcontrolled switches for each pair of stator windings, said controlledswitches being solid state controlled devices, said three opposing pairsof concentrated stator windings have a winding pitch of about 120* andeach stator winding overlaps the adjacent stator windings by about 60*,and said rotor pole faces have a circumferential length of about 60*,whereby the brushless motor is suitable for quasi-square voltage waveshape energization.
 5. A brushless motor suitable for energization bysimple substantially rectilinear voltage wave shapes comprising anannular stator member supporting a plurality of opposing pairs of seriesconnected concentrated stator windings for generating magnetic fields ofopposite polarity in torque producing relation to a ferromagnetic rotormounted for rotation within said stator member, said stator member androtor each having opposing arcuate pole faces to establish anapproximately constant gap width therebetween, the winding pitch andlocation relativE to one another of said concentrated stator windings,and the circumferential length of said rotor pole faces, havinginterdependent angular dimensions to produce simple substantiallyrectilinear back emf voltages in each pair of stator windings that haveapproximately the same wave shape as the energizing rectilinear voltagewave shapes, wherein there are three opposing pairs of concentratedstator windings each having a winding pitch of about 90* and each statorwinding overlaps the adjacent stator windings by about 30*, and saidrotor pole faces have a circumferential length of about 90*, whereby thebrushless motor is suitable for square voltage wave shape energization.6. A brushless motor suitable for energization by simple substantiallyrectilinear voltage wave shapes comprising an annular stator membersupporting a plurality of opposing pairs of series connectedconcentrated stator windings for generating magnetic fields of oppositepolarity in torque producing relation to a ferromagnetic rotor mountedfor rotation within said stator member, said stator member and rotoreach having opposing arcuate pole faces to establish an approximatelyconstant gap width therebetween, the winding pitch and location relativeto one another of said concentrated stator windings, and thecircumferential length of said rotor pole faces, having interdependentangular dimensions to produce simple substantially rectilinear back emfvoltages in each pair of stator windings that have approximately thesame wave shape as the energizing rectilinear voltage wave shapes,wherein there are three opposing pairs of concentrated stator windingseach having a winding pitch of about 120* and each stator windingoverlaps the adjacent stator windings by about 60*, and said rotor polefaces have a circumferential length of about 120*, whereby the brushlessmotor is suitable for stepped wave energization.
 7. A brushless motorsuitable for energization by simple substantially rectilinear voltagewave shapes comprising an annular stator member supporting a pluralityof opposing pairs of series connected concentrated stator windings forgenerating magnetic fields of opposite polarity in torque producingrelation to a ferromagnetic rotor mounted for rotation within saidstator member, said stator member and rotor each having opposing arcuatepole faces to establish an approximately constant gap widththerebetween, the winding pitch and location relative to one another ofsaid concentrated stator windings, and the circumferential length ofsaid rotor pole faces, having interdependent angular dimensions toproduce simple substantially rectilinear back emf voltages in each pairof stator windings that have approximately the same wave shape as theenergizing rectilinear voltage wave shapes, wherein there are threenon-overlapping opposing pairs of concentrated stator windings eachhaving a winding pitch of about 60*, and said rotor pole faces have acircumferential length of about 120*, whereby the brushless motor issuitable for quasi-square wave shape energization.
 8. A brushless motorsuitable for energization by simple substantially rectilinear voltagewave shapes comprising an annular stator member supporting a pluralityof opposing pairs of series connected concentrated stator windings forgenerating magnetic fields of opposite polarity in torque producingrelation to a ferromagnetic rotor mounted for rotation within saidstator member, said stator member and rotor each having opposing arcuatepole faces to establish an approximately constant gap widththerebetween, the winding pitch and location relative to one another ofsaid concentrated stator windings, and the circumferential length ofsaid rotor pole faces, having interdependent angular dimensions toproduce simple substantially rectilinear back emf voltages in each pairof stator windings that have approximately the same wave Shape as theenergizing rectilinear voltage wave shapes, wherein there are threeopposing pairs of concentrated stator windings each having a windingpitch of about 120* and each stator winding overlaps the adjacent statorwindings by about 60*, and said rotor pole faces have a circumferentiallength of about 60*, whereby the brushless motor is suitable forquasi-square wave shape energization.
 9. A compatible brushless motorand motor control circuit comprising an annular stator member supportinga plurality of symmetrically arranged opposing pairs of concentratedstator windings each simultaneously generating magnetic fields ofopposite polarity in torque producing relation to a rotatableferromagnetic rotor, said stator member and rotor having opposingarcuate pole faces to establish an approximately constant gap widththerebetween, a motor control circuit comprising only a few controlledswitches for applying simple substantially rectilinear stepped waveshape energizing voltages of both polarities to said pairs of statorwindings, wherein the sum of the angular dimensions of the winding pitchof said concentrated stator windings and the circumferential length ofone of said rotor pole faces totals approximately 240* and producessubstantially rectilinear back emf voltages in each pair of statorwindings that have approximately the same wave shape as the energizingvoltage applied by said motor control circuit, and control meansresponsive to the instantaneous position of said rotor for renderingconductive said controlled switches for desired intervals of conductionto energize said pairs of stator windings in a sequence to producecontinuous torque to rotate said rotor in a given direction.